Process for coating metallic surfaces with an aqueous composition, and this composition

ABSTRACT

A composition and a method for coating metallic surfaces with a silane/silanol/siloxane/polysiloxane-containing composition, whereby the composition contains a) at least one compound selected from the silanes, silanols, siloxanes and polysiloxanes, b) at least two compounds selected from titanium-, hafnium-, zirconium-, aluminum- or boron-containing compounds, optionally c) at least one type of cation selected from cations of metals of the 1 st  to 3 rd  and 5 th  to 8 th  sub-groups including the lanthanides and the 2 nd  main group of the periodic table of the elements or at least one corresponding compound, d) at least one organic compound selected from monomers, oligomers, polymers, copolymers and block copolymers or e) at least one substance affecting the pH value, water and optionally at least one organic solvent.

This application is a continuation application of U.S. Ser. No.11/667,093 filed Aug. 1, 2007 now abandoned, hereby incorporated byreference in its entirety, which is a §371 of PCT/EP2005/011954 filedNov. 9, 2005, and claims priority from U.S. Ser. No. 10/985,652 filedNov. 10, 2004, German Patent Application No. 10 2005 015 573.1 filedApr. 4, 2005, German Patent Application No. 10 2005 015 576.6 filed Apr.4, 2005 and German Patent Application No. 10 2005 015 575.8 filed Apr.4, 2005.

The invention relates to a process for coating metallic surfaces with anaqueous composition containing at least one silane and/or relatedcompound and at least two other components. The invention furtherrelates to corresponding aqueous compositions and to the use of thesubstrates coated by the process according to the invention.

The processes most commonly employed hitherto for the treatment ofmetallic surfaces, especially parts, coil or coil portions made of atleast one metallic material, or for the pretreatment of metallicsurfaces prior to lacquering are frequently based on the one hand on theuse of chromium(VI) compounds, optionally together with diverseadditives, or on the other hand on phosphates, e.g.zinc/manganese/nickel phosphates, optionally together with diverseadditives.

Because of the toxicological and ecological risks associated especiallywith processes using chromate or nickel, alternatives to these processesin all the areas of surface technology for metallic substrates have beensought for many years, but it has repeatedly been found that, in manyapplications, completely chromate-free or nickel-free processes do notsatisfy 100% of the performance spectrum or do not offer the desiredsafety. Attempts are therefore being made to minimize the chromatecontents or nickel contents and to replace Cr⁶⁺ with Cr³⁺ as far aspossible. High-quality phosphatizing processes are used especially inthe automobile industry, e.g. for the pretreatment of car bodies priorto lacquering, which have maintained the quality of automobile corrosionprotection at a high level. Zinc/manganese/nickel phosphatizingprocesses are conventionally employed for this purpose. Despite manyyears of research and development, attempts to phosphatize nickel-freewithout pronounced quality limitations have proved unsuccessful formultimetal applications such as those often involved in car bodies,where, in Europe, metallic surfaces of steel, galvanized steel andaluminium or aluminium alloys are typically pretreated in the same bath.However, since nickel contents, even if comparatively small, are nowclassified as being of greater toxicological concern for the foreseeablefuture, the question arises as to whether an equivalent corrosionprotection can be achieved with other chemical processes.

The use e.g. of silanes/silanols in aqueous compositions for theproduction of siloxane/polysiloxane-rich anticorrosive coatings is knownin principle. For the sake of simplicity,silane/silanol/siloxane/polysiloxane will hereafter often be referred toonly as silane. These coatings have proved themselves, but someprocesses for coating with an aqueous composition containingpredominantly silane, in addition to solvent(s), are difficult to apply.These coatings are not always formed with outstanding properties.Moreover, adequate characterization, with the naked eye or optical aids,of the very thin, transparent silane coatings on the metallic substrate,and their defects, can be problematic. The corrosion protection and thelacquer adhesion of the siloxane- and/or polysiloxane-rich coatingsformed are often high, but not always; in some cases, even withappropriate application, they are insufficiently high for particularuses. There is a need for other processes, using at least one silane,which offer a high process safety and a high quality of the coatingsproduced, especially in respect of corrosion resistance and lacqueradhesion.

In the formulation of silane-containing aqueous compositions, it hasalso proved beneficial to add a small or large amount of at least onecomponent selected from the group comprising organic monomers, oligomersand polymers. The type and amount of silane added to such compositionsis in some cases of decisive importance for the outcome. Conventionally,however, the amounts of silane added are comparatively small—usuallyonly up to 5 wt. % of the total solids content—and they then function asa coupling agent, where the adhesion-promoting action should prevailespecially between metallic substrate and lacquer and optionally betweenpigment and organic lacquer constituents, but a slight crosslinkingaction can also occur in some cases as a secondary effect. Chiefly, verysmall amounts of silane are added to thermosetting resin systems.

The other two patent applications on a similar subject matter submittedto the same patent office on the same date are expressly included here,especially in respect of the aqueous compositions, the additions to theaqueous compositions, the steps before, during and after coating, thebath behaviour, the layer formation, the layer properties and theeffects determined, particularly in the Examples and ComparativeExamples. Likewise, the patent applications that give rise to a right ofpriority are also expressly included in the subsequent patentapplications.

It is known from EP 1 017 880 B1 to use an aqueous compositioncontaining a partially hydrolysed aminosilane and a fluorine-containingacid in a mixing ratio of 1:2 to 2:1. This acid is preferablyfluorotitanic acid. The coatings produced therewith are good but do notsatisfy the prerequisites for high-quality corrosion-resistant coatingsin the same way as the extremely high-quality phosphate coatings basedon zinc/manganese/nickel phosphate used in automobile construction,especially for multimetal applications. The publication gives noindication that a combination of several acids can be advantageous.

The object was therefore to propose aqueous compositions whose coatingshave an environmentally friendly chemical composition and assure a highcorrosion resistance, and which are also suitable in multimetalapplications in which e.g. steel and zinc-rich metallic surfaces, andoptionally also aluminium-rich metallic surfaces, are treated orpretreated in the same bath. The object was also to propose aqueouscompositions that are suitable for coating car bodies in automobileconstruction.

It has now been found that a combination of at least two complexfluorides, especially fluorotitanic acid and fluorozirconic acid,affords an exceptional increase in quality of the coating.

It has now been found not only that it is possible to rinse freshlyapplied silane-based coatings that have not yet dried thoroughly andhence not yet condensed more substantially, but also that this processsequence is even advantageous, because the coatings produced and rinsedin this way even have better corrosion protection and better lacqueradhesion, to some extent independently of the chemical composition ofthe aqueous bath. This contradicts earlier experiences where the rinsingof a freshly applied silane-based coating that has not yet dried moresubstantially easily and frequently leads to an impairment of thequality of the layer, or even to the removal of part or, occasionally,all of the coating.

It has now also been found that it is possible and advantageous to applya lacquer, a lacquer-like coating, a primer or an adhesive to freshlyapplied silane-based coatings that have not yet dried thoroughly andhence not yet condensed more substantially, which may also have beenrinsed in this state. The application of such compositions tosilane-based wet films is advantageous because the coatings produced andrinsed in this way even have better corrosion protection and betterlacquer adhesion, to some extent independently of the chemicalcomposition of the aqueous bath.

The object is achieved by a process for coating metallic surfaces with acomposition containing silane/silanol/siloxane/polysiloxane, thecomposition consisting essentially of

-   -   a) at least one compound selected from silanes, silanols,        siloxanes and polysiloxanes,    -   b) at least two compounds selected from compounds containing        titanium, hafnium, zirconium, aluminium and/or boron, and        optionally    -   c) at least one type of cation selected from cations of metals        of subgroups 1 to 3 and 5 to 8, including lanthanides, and of        main group 2 of the periodic table of the elements, and/or at        least one corresponding compound,    -   d) at least one organic compound selected from monomers,        oligomers, polymers, copolymers and block copolymers, and/or    -   e) at least one substance that influences the pH, as well as    -   f) water, and    -   g) optionally at least one organic solvent.

The object is also achieved with an aqueous composition for coatingmetallic surfaces which consists essentially of

-   -   a) at least one compound selected from silanes, silanols,        siloxanes and polysiloxanes, and    -   b) at least two compounds containing titanium, hafnium,        zirconium, aluminium and/or boron, and optionally    -   c) at least one type of cation selected from cations of metals        of subgroups 1 to 3 and 5 to 8, including lanthanides, and of        main group 2 of the periodic table of the elements, and/or at        least one corresponding compound,    -   d) at least one organic compound selected from monomers,        oligomers, polymers, copolymers and block copolymers, and/or    -   e) at least one substance that influences the pH, as well, as    -   f) water, and    -   g) optionally at least one organic solvent.

The content of the patent application that gives rise to a right ofpriority to the present patent application, DE 102005015575.8, thecontent of the other, related patent applications that give rise to aright of priority, DE 102005015573.1, DE 102005015576.6 and U.S. Ser.No. 10/985,652, and the content of the parallel PCT applications issuingfrom the three last-mentioned patent applications that give rise to aright of priority, is to be expressly included in the present patentapplication, especially in respect of the different compositions,different compounds added, different process steps, different coatingsproduced, Examples, Comparative Examples and effects, properties andlaboratory results mentioned therein.

The word “silane” is used here for silanes, silanols, siloxanes,polysiloxanes and their reaction products or derivatives, which oftenare also “silane” mixtures. In terms of the present patent application,the word “condensation” denotes all forms of crosslinking, furthercrosslinking and further chemical reactions of thesilanes/silanols/siloxanes/polysiloxanes. In terms of the present patentapplication, the word “coating” refers to the coating formed with theaqueous composition, including the wet film, the dried-on film, thethoroughly dried film, the film dried at elevated temperature and thefilm optionally crosslinked further by heating and/or irradiation.

In terms of the present patent application, the expression “consistsessentially of . . . ” is understood as meaning that the aqueouscomposition according to the invention can optionally comprise up to 15wt. %, based on the content of solids and active ingredients ofsubstances a) to d) and f), of other substances that can help to improvethe very wide variety of properties of the aqueous composition and/orthe coating, and/or to adapt them to requirements. These substances caninclude especially additives such as biocide(s) and/or defoamers and/orat least one substance selected from silicon-free compounds having atleast one amino, urea and/or ureido group, hydroxide(s), carboxylate(s),nitrate (s) and phosphorus-containing and oxygen-containing compounds,e.g. phosphate(s). This expression preferably comprises, within the upto 15 wt. % of the content of solids and active ingredients ofsubstances a) to d) and f), other substances that essentially are onlyhydroxide(s), acetate(s) and nitrate(s). Particularly preferably, thecontent of the other substances is up to 12, up to 10, up to 8, up to 6,up to 4 or up to 2 wt. % of the content of solids and active ingredientsof substances a) to d) and f).

The aqueous composition is an aqueous solution, an aqueous dispersionand/or an emulsion. The pH of the aqueous composition is preferablygreater than 1.5 and less than 9, particularly preferably in the rangefrom 2 to 7, very particularly preferably in the range from 2.5 to 6.5and especially in the range from 3 to 6.

Particularly preferably, at least one silane and/or at least onecorresponding compound having at least one amino group, urea groupand/or ureido group (imino group) is added to the aqueous compositionbecause the coatings produced therewith often exhibit a greater lacqueradhesion and/or a higher affinity for the subsequent lacquer layer. Inparticular, when using at least one silane and/or at least onecorresponding compound having at least one such group, it should bepointed out that condensation may proceed very rapidly at pH valuesbelow 2. The proportion of aminosilanes, ureidosilanes and/or silaneshaving at least one ureido group, and/or of corresponding silanols,siloxanes and polysiloxanes, relative to the sum of all types ofcompounds selected from silanes, silanols, siloxanes and polysiloxanes,can preferably be high, particularly preferably above 20, above 30 orabove 40 wt. %, calculated as the corresponding silanols, veryparticularly preferably above 50, above 60, above 70 or above 80 wt. %and possibly even up to 90, up to 95 or up to 100 wt. %.

Preferably, the aqueous composition has a content ofsilane/silanol/siloxane/polysiloxane a) ranging from 0.005 to 80 g/l,calculated on the basis of the corresponding silanols. This content isparticularly preferably in the range from 0.01 to 30 g/l, veryparticularly preferably in the range from 0.02 to 12 g/l, to 8 g/l or to5 g/l and especially in the range from 0.05 to 3 g/l or in the rangefrom 0.08 to 2 g/l or to 1 g/l. These ranges of contents referparticularly to bath compositions.

However, if a concentrate is used to prepare a corresponding bathcomposition, especially by dilution with water and optionally by theaddition of at least one other substance, it is advisable, for example,to keep a concentrate A containing silane/silanol/siloxane/polysiloxanea) separate from a concentrate B containing all or almost all of theremaining constituents, and only to bring these components together inthe bath. This optionally also makes it possible for at least onesilane, silanol, siloxane and/or polysiloxane to be partially orcompletely in the solid state, to be added in the solid state and/or tobe added as a dispersion or solution. The content ofsilane/silanol/siloxane/polysiloxane a) in concentrate A preferablyranges from 0.01 to 1000 g/l, calculated on the basis of thecorresponding silanols. This content ranges particularly preferably from0.02 to 200 g/l, very particularly preferably from 0.05 to 120 g/l andespecially from 0.1 to 60 g/l. However, the main emphases of thecontents in the concentration ranges of concentrate A or the bath canvary with the application.

Particularly preferably, the composition contains at least one silane,silanol, siloxane and/or polysiloxane a) having in each case at leastone group selected from acrylate groups, alkylaminoalkyl groups,alkylamino groups, amino groups, aminoalkyl groups, succinic anhydridegroups, carboxyl groups, epoxy groups, glycidoxy groups, hydroxylgroups, urea groups, isocyanato groups, methacrylate groups and/orureido groups (imino groups).

The silanes, silanols, siloxanes and/or polysiloxanes in the aqueouscomposition, or at least their compounds added to the aqueouscomposition, or at least some of these, are preferably water-soluble. Interms of the present patent application, the silanes are regarded aswater-soluble if together they have a solubility in water of at least0.05 g/l, preferably of at least 0.1 g/l and particularly preferably ofat least 0.2 g/l or at least 0.3 g/l at room temperature in thecomposition containing silane/silanol/siloxane/polysiloxane. This doesnot mean that each individual silane must have this minimum solubility,but that these minimum values are achieved on average.

The aqueous composition preferably contains at least onesilane/silanol/siloxane/polysiloxane selected from fluorine-free silanesand the corresponding silanols/siloxanes/polysiloxanes, consistingrespectively of at least one acyloxysilane, alkoxysilane, silane havingat least one amino group, such as an aminoalkylsilane, silane having atleast one succinic acid group and/or succinic anhydride group,bis(silyl)silane, silane having at least one epoxy group, such as aglycidoxy-silane, (meth)acrylatosilane, poly(silyl)silane, ureidosilaneor vinylsilane, and/or at least one silanol and/or at least one siloxaneor polysiloxane whose chemical composition corresponds to that of thesilanes mentioned above. It contains at least one silane and/or (in eachcase) at least one monomeric, dimeric, oligomeric and/or polymericsilanol and/or (in each case) at least one monomeric, dimeric,oligomeric and/or polymeric siloxane, oligomers being understoodhereafter to include dimers and trimers. Particularly preferably, the atleast one silane or the corresponding silanol/siloxane/polysiloxane hasin each case at least one amino group, urea group and/or ureido group.

In particular, this composition contains at least one silane and/or atleast one corresponding silanol/siloxane/polysiloxane selected from thefollowing group or based thereon:

-   (3,4-epoxyalkyl)trialkoxysilane,-   (3,4-epoxycycloalkyl)alkyltrialkoxysilane,-   3-acryloxyalkyltrialkoxysilane,-   3-glycidoxyalkyltrialkoxysilane,-   3-methacryloxyalkyltrialkoxysilane,-   3-(trialkoxysilyl)alkylsuccinosilane,-   4-aminodialkylalkyltrialkoxysilane,-   4-aminodialkylalkylalkyldialkoxysilane,-   aminoalkylaminoalkyltrialkoxysilane,-   aminoalkylaminoalkylalkyldialkoxysilane,-   aminoalkyltrialkoxysilane,-   bis(trialkoxysilylalkyl)amine,-   bis(trialkoxysilyl)ethane,-   gamma-acryloxyalkyltrialkoxysilane,-   gamma-aminoalkyltrialkoxysilane,-   gamma-methacryloxyalkyltrialkoxysilane,-   (gamma-trialkoxysilylalkyl)dialkylenetriamine,-   gamma-ureidoalkyltrialkoxysilane,-   N-2-aminoalkyl-3-aminopropyltrialkoxysilane,-   N-(3-trialkoxysilylalkyl)alkylenediamine,-   N-alkylaminoisoalkyltrialkoxysilane,-   N-(aminoalkyl)aminoalkylalkyldialkoxysilane,-   N-beta-(aminoalkyl)-gamma-aminoalkyltrialkoxysilane,-   N-(gamma-trialkoxysilylalkyl)dialkylenetriamine,-   N-phenylaminoalkyltrialkoxysilane,-   poly(aminoalkyl)alkyldialkoxysilane,-   tris(3-trialkoxysilyl)alkylisocyanurate,-   ureidoalkyltrialkoxysilane and-   vinylacetoxysilane.

Particularly preferably, this composition contains at least one silaneand/or at least one corresponding silanol/siloxane/polysiloxane selectedfrom the following group or based thereon:

-   (3,4-epoxybutyl)triethoxysilane,-   (3,4-epoxybutyl)trimethoxysilane,-   (3,4-epoxycyclohexyl)propyltriethoxysilane,-   (3,4-epoxycyclohexyl)propyltrimethoxysilane,-   3-acryloxypropyltriethoxysilane,-   3-acryloxypropyltrimethoxysilane,-   3-glycidoxypropyltriethoxysilane,-   3-glycidoxypropyltrimethoxysilane,-   3-methacryloxypropyltriethoxysilane,-   3-methacryloxypropyltrimethoxysilane,-   3-(triethoxysilyl)propylsuccinosilane,-   aminoethylaminopropylmethyldiethoxysilane,-   aminoethylaminopropylmethyldimethoxysilane,-   aminopropyltrialkoxysilane,-   beta-(3,4-epoxycyclohexyl)ethyltriethoxysilane,-   beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,-   beta-(3,4-epoxycyclohexyl)methyltriethoxysilane,-   beta-(3,4-epoxycyclohexyl)methyltrimethoxysilane,-   bis-1,2-(triethoxysilyl)ethane,-   bis-1,2-(trimethoxysilyl)ethane,-   bis(triethoxysilylpropyl)amine,-   bis(trimethoxysilylpropyl)amine,-   gamma-(3,4-epoxycyclohexyl)propyltriethoxysilane,-   gamma-(3,4-epoxycyclohexyl)propyltrimethoxysilane,-   gamma-acryloxypropyltriethoxysilane,-   gamma-acryloxypropyltrimethoxysilane,-   gamma-aminopropyltriethoxysilane,-   gamma-aminopropyltrimethoxysilane,-   gamma-methacryloxypropyltriethoxysilane,-   gamma-methacryloxypropyltrimethoxysilane,-   gamma-ureidopropyltrialkoxysilane,-   N-2-aminoethyl-3-aminopropyltriethoxysilane,-   N-2-aminoethyl-3-aminopropyltrimethoxysilane,-   N-2-aminomethyl-3-aminopropyltriethoxysilane,-   N-2-aminomethyl-3-aminopropyltrimethoxysilane,-   N-(3-(trimethoxysilyl)propyl)ethylenediamine,-   N-beta-(aminoethyl)-gamma-aminopropyltriethoxysilane,-   N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane,-   N-(gamma-triethoxysilylpropyl)diethylenetriamine,-   N-(gamma-trimethoxysilylpropyl)diethylenetriamine,-   N-(gamma-triethoxysilylpropyl)dimethylenetriamine,-   N-(gamma-trimethoxysilylpropyl)dimethylenetriamine,-   poly(aminoalkyl)ethyldialkoxysilane,-   poly(aminoalkyl)methyldialkoxysilane,-   tris(3-(triethoxysilyl)propyl)isocyanurate,-   tris(3-(trimethoxysilyl)propyl)isocyanurate,-   ureidopropyltrialkoxysilane and-   vinyltriacetoxysilane.

Optionally, in specific embodiments, the aqueous composition contains atleast one silane/silanol/siloxane/polysiloxane having afluorine-containing group. By choosing the silane compound(s) it is alsopossible to adjust the hydrophilicity/hydrophobicity according to thedesired objective.

Preferably, in some embodiments of the aqueous composition, at least oneat least partially hydrolysed and/or at least partially condensedsilane/silanol/siloxane/polysiloxane is added. In particular, whenmixing the aqueous composition, it is optionally possible to add atleast one already prehydrolysed, precondensedsilane/silanol/siloxane/polysiloxane. Such an addition is particularlypreferred.

In some embodiments, at least one at least extensively and/or completelyhydrolysed and/or at least extensively and/or completely condensedsilane/silanol/siloxane/polysiloxane can be added to the aqueouscomposition. In many embodiments, a non-hydrolysed silane bonds to themetallic surface less well than an at least partially hydrolysedsilane/silanol. In many embodiments, an extensively hydrolysed anduncondensed or only slightly condensed silane/silanol/siloxane bonds tothe metallic surface markedly better than an at least partiallyhydrolysed and extensively condensedsilane/silanol/siloxane/polysiloxane. In many embodiments, a completelyhydrolysed and extensively condensed silanol/siloxane/polysiloxaneexhibits only a slight tendency to become chemically bonded to themetallic surface.

In some embodiments, at least one siloxane and/or polysiloxanecontaining little or no silanes/silanols—e.g. less than 20 or less than40 wt. % of the sum of silane/silanol/siloxane/polysiloxane—can be addedto the aqueous composition in addition and/or as an alternative tosilane(s)/silanol(s). The siloxane or polysiloxane is preferablyshort-chain and is preferably applied by means of a rollcoatertreatment. This then optionally affects the coating by strengthening thehydrophobicity and increasing the blank corrosion protection.

Preferably, the aqueous composition contains at least two or even atleast three titanium, hafnium, zirconium, aluminium and boron compounds,it being possible for these compounds to differ in their cations and/oranions. The aqueous composition, especially the bath composition,preferably contains at least one complex fluoride b) and particularlypreferably at least two complex fluorides selected from complexfluorides of titanium, hafnium, zirconium, aluminium and boron.Preferably, their difference lies not only in the type of complex. Theaqueous composition, especially the bath composition, preferably has acontent of compounds b), selected from titanium, hafnium, zirconium,aluminium and boron compounds, ranging from 0.01 to 50 g/l, calculatedas the sum of the corresponding metals. This content ranges particularlypreferably from 0.1 to 30 g/l, very particularly preferably from 0.3 to15 g/l and especially from 0.5 to 5 g/l. On the other hand, the contentof titanium, hafnium, zirconium, aluminium and boron compounds in theconcentrate, for example in concentrate B free ofsilane/silanol/siloxane/polysiloxane, can preferably range from 1 to 300g/l, calculated as the sum of the corresponding metals. This contentranges particularly preferably from 2 to 250 g/l, very particularlypreferably from 3 to 200 g/l and especially from 5 to 150 g/l. Thecomposition preferably contains no aluminium phosphate, no titaniumsulfate, no zirconium nitrate and/or no zirconium chloride.

Preferably, the composition contains at least one complex fluoride, thecontent of complex fluoride (s) ranging especially from 0.01 to 100 g/l,calculated as the sum of the corresponding metal complex fluorides asMeF₆. This content ranges preferably from 0.03 to 70 g/l, particularlypreferably from 0.06 to 40 g/l and very particularly preferably from 1to 10 g/l. The complex fluoride can be present especially as MeF₄ and/orMeF₆, but also in other states or intermediate states. Advantageously,at least one titanium complex fluoride and at least one zirconiumcomplex fluoride are simultaneously present in many embodiments. It canbe advantageous in many cases here to have at least one MeF₄ complex andat least one MeF₆ complex present in the composition simultaneously,especially a TiF₆ complex and a ZrF₄ complex. It can be advantageoushere to adjust these proportions of complex fluorides in the concentrateand transfer them to the bath in this way. On the other hand, thecontent of these compounds in the concentrate, for example inconcentrate B free of silane/silanol/siloxane/polysiloxane, canpreferably range from 0.05 to 500 g/l, calculated as the sum of MeF₆.This content ranges particularly preferably from 0.05 to 300 g/l, veryparticularly preferably from 0.05 to 150 g/l and especially from 0.05 to50 g/l.

Surprisingly, the individual complex fluorides do not adversely affectone another when combined, but exhibit an unexpected positivereinforcing effect. These additions based on complex fluoride obviouslyact in a similar or identical manner. Surprisingly, if a combination ofcomplex fluorides based on titanium and zirconium is used rather than acomplex fluoride based only on titanium or only on zirconium, theresults obtained are always noticeably better than in the case of onlyone of these additions. A complex fluoride based on titanium orzirconium probably deposits on the surface as oxide and/or hydroxide.

It has now been established, surprisingly, that a good multimetaltreatment with a single aqueous composition is only possible if acomplex fluoride has been used, and that a very good multimetaltreatment with a single aqueous composition is only possible if at leasttwo different complex fluorides are used, e.g. those based on titaniumand zirconium. In a very wide variety of experiments, the complexfluorides used individually never gave results equivalent to those forthe combination of these two complex fluorides, independently of whatother additions were made.

As an alternative or in addition to at least one complex fluoride, it isalso possible to add another type of titanium, hafnium, zirconium,aluminium and/or boron compound, for example at least onehydroxycarbonate and/or at least one other water-soluble or sparinglywater-soluble compound, e.g. at least one nitrate and/or at least onecarboxylate.

It has now been shown, however, that an addition of silicon hexafluorideas the only complex fluoride added to an aqueous composition has adifferent and sometimes markedly poorer effect than the additions ofother complex fluorides.

Preferably, only types of cation, or corresponding compounds, from thegroup comprising magnesium, calcium, yttrium, lanthanum, cerium,vanadium, niobium, tantalum, molybdenum, tungsten, manganese, iron,cobalt, nickel, copper, silver and zinc, and particularly preferablyfrom the group comprising magnesium, calcium, yttrium, lanthanum,cerium, vanadium, molybdenum, tungsten, manganese, iron, cobalt, copperand zinc, are selected as cations and/or corresponding compounds c),trace contents being excepted.

On the other hand, it has been shown, surprisingly, that iron and zinccations, and therefore also the presence in the bath of correspondingcompounds which can make an increased contribution, in the particularcase of acidic compositions, to dissolving such ions out of the metallicsurface, do not have an adverse effect, over wide ranges of contents, onthe bath behaviour, the layer formation or the layer properties.

Preferably, the aqueous composition, especially the bath composition,has a content of cations and/or corresponding compounds c) ranging from0.01 to 20 g/l, calculated as the sum of the metals. This content rangesparticularly preferably from 0.03 to 15 g/l, very particularlypreferably from 0.06 to 10 g/l and especially from 0.1 to 6 g/l. On theother hand, the content of these compounds in the concentrate, forexample in concentrate B free of silane/silanol/siloxane/polysiloxane,can preferably range from 1 to 240 g/l, calculated as the sum of themetals. This content ranges particularly preferably from 2 to 180 g/l,very particularly preferably from 3 to 140 g/l and especially from 5 to100 g/l.

The composition preferably contains at least one type of cation selectedfrom cations of cerium, chromium, iron, calcium, cobalt, copper,magnesium, manganese, molybdenum, nickel, niobium, tantalum, yttrium,zinc, tin and other lanthanides, and/or at least one correspondingcompound. Preferably, not all the cations present in the aqueouscomposition have been not only dissolved out of the metallic surface bythe aqueous composition, but also at least partially or even extensivelyadded to the aqueous composition. A freshly prepared bath can thereforebe free of certain cations or compounds which are only freed or formedfrom reactions with metallic materials or from reactions in the bath.

Surprisingly, the addition of manganese ions or at least one manganesecompound has been shown to be particularly advantageous. Althoughapparently no manganese compound or almost no manganese compound isdeposited on the metallic surface, this addition clearly promotes thedeposition of silane/silanol/siloxane/polysiloxane, therebysignificantly improving the properties of the coating. Unexpectedly, anaddition of magnesium ions or at least one magnesium compound has alsobeen shown to be advantageous, since this addition promotes thedeposition of titanium and/or zirconium compounds, probably as oxideand/or hydroxide, on the metallic surface and thus markedly improves theproperties of the coating. A combined addition of magnesium andmanganese improves the coatings still further in some cases. Bycontrast, an addition of only 0.02 g/l of copper ions has not yet beenshown to have a significant influence. If the calcium ion content isincreased, care should be taken to ensure that a complex fluoride is notdestabilized by the formation of calcium fluoride.

Preferably, the composition has a content of at least one type of cationand/or corresponding compounds, selected from alkaline earth metal ions,ranging from 0.01 to 50 g/l, calculated as corresponding compounds,particularly preferably from 0.03 to 35 g/l, very particularlypreferably from 0.06 to 20 g/l and especially from 0.1 to 8 g/l. Thealkaline earth metal ions or corresponding compounds can help toreinforce the deposition of compounds based on titanium and/orzirconium, which is often advantageous especially for increasing thecorrosion resistance. On the other hand, the content of these compoundsin the concentrate, for example in concentrate B free ofsilane/silanol/siloxane/polysiloxane, can range preferably from 0.1 to100 g/l, calculated as the sum of the corresponding compounds,particularly preferably from 0.3 to 80 g/l, very particularly preferablyfrom 0.6 to 60 g/l and especially from 0.5 to 30 g/l.

Preferably, the composition has a content of at least one type ofcation, selected from cations of iron, cobalt, magnesium, manganese,nickel, yttrium, zinc and lanthanides, and/or of at least onecorresponding compound c), ranging especially from 0.01 to 20 g/l,calculated as the sum of the metals. This content ranges particularlypreferably from 0.03 to 15 g/l, very particularly preferably from 0.06to 10 g/l and especially from 0.1 to 6 g/l. On the other hand, thecontent of these compounds in the concentrate, for example inconcentrate B free of silane/silanol/siloxane/polysiloxane, canpreferably range from 1 to 240 g/l, calculated as the sum of the metals.This content ranges particularly preferably from 2 to 180 g/l, veryparticularly preferably from 3 to 140 g/l and especially from 5 to 100g/l.

Preferably, the composition contains at least one organic compound d)selected from monomers, oligomers, polymers, copolymers and blockcopolymers, especially at least one compound based on acrylic, epoxideand/or urethane. At least one organic compound having at least one silylgroup can also be used here, in addition or as an alternative. It ispreferred in some embodiments to use such organic compounds having acontent or a higher content of OH groups, amine groups, carboxylategroups, isocyanate groups and/or isocyanurate groups.

Preferably, the composition has a content of at least one organiccompound d), selected from monomers, oligomers, polymers, copolymers andblock copolymers, ranging from 0.01 to 200 g/l, calculated as addedsolids. This content ranges particularly preferably from 0.03 to 120g/l, very particularly preferably from 0.06 to 60 g/l and especiallyfrom 0.1 to 20 g/l. In some embodiments, such organic compounds can helpto homogenize the formation of the coating. These compounds cancontribute to the formation of a more compact, denser, more chemicallyresistant and/or more water-resistant coating, compared with coatingsbased on silane/silanol/siloxane/polysiloxane etc. without thesecompounds. The hydrophilicity/hydrophobicity can also be adjustedaccording to the desired objective by the choice of organic compound(s).However, a strongly hydrophobic coating is problematic in someapplications because of the required bonding of especially water-basedlacquers, although a stronger hydrophobicity can be established in thecase of powder coatings in particular. When using an addition of atleast one organic compound, a combination with compounds having acertain functionality can prove particularly advantageous, examplesbeing compounds based onamines/diamines/polyamines/urea/imines/diimines/polyimines orderivatives thereof, compounds based in particular on cappedisocyanate/isocyanurate/melamine compounds, and compounds with carboxyland/or hydroxyl groups, e.g. carboxylates, longer-chain sugar-likecompounds, e.g. (synthetic) starch, cellulose, saccharides, long-chainalcohols and/or derivatives thereof. The long-chain alcohols added areespecially those having 4 to 20 C atoms, such as a butanediol, a butylglycol, a butyl diglycol, an ethylene glycol ether such as ethyleneglycol monobutyl ether, ethylene glycol monoethyl ether, ethylene glycolmonomethyl ether, ethyl glycol propyl ether, ethylene glycol hexylether, diethylene glycol methyl ether, diethylene glycol ethyl ether,diethylene glycol butyl ether, diethylene glycol hexyl ether, or apropylene glycol ether such as propylene glycol monomethyl ether,dipropylene glycol monomethyl ether, tripropylene glycol monomethylether, propylene glycol monobutyl ether, dipropylene glycol monobutylether, tripropylene glycol monobutyl ether, propylene glycol monopropylether, dipropylene glycol monopropyl ether, tripropylene glycolmonopropyl ether or propylene glycol phenyl ether, trimethylpentanedioldiisobutyrate, a polytetrahydrofuran, a polyetherpolyol and/or apolyesterpolyol.

The weight ratio of compounds based onsilane/silanol/siloxane/polysiloxane, calculated on the basis of thecorresponding silanols, to compounds based on organic polymers,calculated as added solids, in the composition, ranges preferably from1:0.05 to 1:3, particularly preferably from 1:0.1 to 1:2 and veryparticularly preferably from 1:0.2 to 1:1. In some embodiments, thisratio ranges preferably from 1:0.05 to 1:30, particularly preferablyfrom 1:0.1 to 1:2, very particularly preferably from 1:0.2 to 1:20 andespecially from 1:0.25 to 1:12, from 1:0.3 to 1:8 or from 1:0.35 to 1:5.

It has now been found, surprisingly, that an addition of organic polymerand/or copolymer, in particular, markedly improves the corrosionresistance, especially on iron and steel, and is of particular advantagefor a higher process safety and constantly good coating properties.

Acetic acid, for example, can be added as a catalyst for the hydrolysisof a silane. The pH of the bath can be raised e.g. with ammonia/ammoniumhydroxide, an alkali-metal hydroxide and/or a compound based on amine,such as monoethanolamine, while the pH of the bath is preferably loweredwith acetic acid, hydroxyacetic acid and/or nitric acid. Such additionsbelong to the substances that influence the pH.

The composition optionally has a content of silicon-free compoundshaving at least one amino, urea and/or ureido group, especiallyamine/diamine/polyamine/urea/imine/diimine/polyimine compounds andderivatives thereof, ranging preferably from 0.01 to 10 g/l, calculatedas the sum of the corresponding compounds. This content rangesparticularly preferably from 0.03 to 7 g/l, very particularly preferablyfrom 0.06 to 4 g/l and especially from 0.1 to 1 g/l. It is preferable toadd at least one compound such as aminoguanidine, monoethanolamine,triethanolamine and/or a branched urea derivative with an alkyl radical.An addition of aminoguanidine, for example, markedly improves theproperties of the coatings according to the invention.

On the other hand, the composition can also contain nitroguanidine. Ithas now been found, surprisingly, that an addition of nitroguanidine, inparticular, to the aqueous composition makes the appearance of thecoatings according to the invention very homogeneous and perceptiblyincreases the coating quality. This has a very positive effectespecially on “sensitive” metallic surfaces such as sand-blasted iron orsteel surfaces. An addition of nitroguanidine noticeably improves theproperties of the coatings according to the invention. A content ofnitrite can markedly reduce the rusting tendency particularly of steelsurfaces. It has now been found, unexpectedly, that an addition ofhydrogen peroxide to the aqueous composition according to the inventionimproves the optical quality of the coated substrates.

Optionally, the composition also contains phosphorus-containingcompounds, especially as oxyanions and/or corresponding compounds, butpreferably no aluminium phosphate. This content ranges particularlypreferably from 0.05 to 8 g/l, very particularly preferably from 0.1 to5 g/l and especially from 0.2 to 2 g/l. These compounds can be at leastone orthophosphate, at least one oligomeric and/or polymeric phosphateand/or at least one phosphonate. The at least one orthophosphate and/orsalts thereof and/or esters thereof can be e.g. at least onealkali-metal phosphate, at least one orthophosphate containing iron,manganese and/or zinc, and/or at least one of their salts and/or esters.Instead or in addition, it is also possible to add in each case at leastone metaphosphate, polyphosphate, pyrophosphate, triphosphate and/orsalts thereof and/or esters thereof. As phosphonate it is possible toadd e.g. at least one phosphonic acid, such as at least onealkyldiphosphonic acid, and/or salts thereof and/or esters thereof. Ithas now been found, surprisingly, that an addition of orthophosphate tothe aqueous composition according to the invention markedly improves thequality of the coatings, especially on electro-galvanized substrates.The phosphorus-containing compounds of this group of substances are notsurfactants.

Optionally, the aqueous composition contains at least one type of anionselected from carboxylates, e.g. acetate, butyrate, citrate, formate,fumarate, glycolate, hydroxyacetate, lactate, laurate, maleate,malonate, oxalate, propionate, stearate and tartrate, and/or at leastone corresponding undissociated and/or only partially dissociatedcompound.

Preferably, the composition has a content of carboxylate anions and/orcarboxylate compounds ranging from 0.01 to 3 g/l, calculated as the sumof the corresponding compounds. This content ranges particularlypreferably from 0.05 to 1.5 g/l, very particularly preferably from 0.1to 0.8 g/l and especially from 0.15 to 0.6 g/l. Particularly preferably,in each case at least one citrate, lactate, oxalate and/or tartrate canbe added as carboxylate. The addition of at least one carboxylate canhelp to complex a cation and keep it in solution more easily, therebymaking it possible to increase the stability and controllability of thebath. Surprisingly, it has been found that the bonding of a silane tothe metallic surface can in some cases be facilitated and improved by acarboxylate content.

Optionally, the composition also contains nitrate. The nitrate contentpreferably ranges from 0.01 to 2 g/l, calculated as the sum of thecorresponding compounds. This content ranges particularly preferablyfrom 0.03 to 1.2 g/l, very particularly preferably from 0.06 to 0.8 g/land especially from 0.1 to 3.5 g/l. Nitrate can help to homogenize theformation of the coating, especially on steel. Nitrite may be convertedto nitrate, usually only partially. Nitrate can be added especially asan alkali-metal nitrate, ammonium nitrate, a heavy metal nitrate, nitricacid and/or a corresponding organic compound. The nitrate can markedlyreduce the rusting tendency, especially on steel and iron surfaces. Thenitrate can optionally contribute to the formation of a defect-freecoating and/or an exceptionally even coating that may be free ofoptically recognizable marks.

Optionally, the composition contains at least one type of cationselected from alkali-metal ions, ammonium ions and correspondingcompounds, especially potassium and/or sodium ions, or at least onecorresponding compound.

Optionally, the composition has a free fluoride content ranging from0.001 to 3 g/l, calculated as F⁻. This content ranges preferably from0.01 to 1 g/l, particularly preferably from 0.02 to 0.5 g/l and veryparticularly preferably up to 0.1 g/l. It has been determined that it isadvantageous in many embodiments to have a low free fluoride content inthe bath because the bath can then be stabilized in many embodiments. Anexcessively high free fluoride content can sometimes adversely affectthe deposition rate of cations. In addition, undissociated and/oruncomplexed fluoride can also occur in many cases, especially in therange from 0.001 to 0.3 g/l. On the other hand, the content of thesecompounds in the concentrate, for example in concentrate B free ofsilane/silanol/siloxane/polysiloxane, can preferably range from 0.05 to5 g/l, calculated as the sum of MeF₆. This content ranges particularlypreferably from 0.02 to 3 g/l, very particularly preferably from 0.01 to2 g/l and especially from 0.005 to 1 g/l. Such an addition is preferablymade in the form of hydrofluoric acid and/or its salts.

Optionally, the composition has a content of at least onefluoride-containing compound and/or fluoride anions, calculated as F⁻and without including complex fluorides, especially at least onefluoride from alkali metal fluoride(s), ammonium fluoride and/orhydrofluoric acid, ranging particularly preferably from 0.001 to 12 g/l,very particularly preferably from 0.005 to 8 g/l and especially from0.01 to 3 g/l. The fluoride ions or corresponding compounds can help tocontrol the deposition of the metal ions on the metallic surface sothat, for example, the deposition of the at least one zirconium compoundcan be increased or decreased as required. On the other hand, thecontent of these compounds in the concentrate, for example inconcentrate B free of silane/silanol/siloxane/polysiloxane, canpreferably range from 0.1 to 100 g/l, calculated as the sum of thecorresponding compounds. This content ranges particularly preferablyfrom 0.3 to 80 g/l, very particularly preferably from 0.6 to 60 g/l andespecially from 1 to 30 g/l. The weight ratio of the sum of the complexfluorides, calculated as the sum of the associated metals, to the sum ofthe free fluorides, calculated as F⁻, is preferably greater than 1:1,particularly preferably greater than 3:1, very particularly preferablygreater than 5:1 and especially greater than 10:1.

In the process according to the invention, the aqueous composition canoptionally contain at least one compound selected from alkoxides,carbonates, chelates, surfactants and additives, e.g., biocides and/ordefoamers.

The aforementioned additions normally have a beneficial effect in theaqueous compositions according to the invention in that they help tofurther improve the good properties of the aqueous base compositionaccording to the invention consisting of components a), b) andsolvent(s). These additions normally act in the same way if only onetitanium compound or only one zirconium compound, or a combinationthereof, is used. However, it has been shown, surprisingly, that thecombination of at least one titanium compound and at least one zirconiumcompound, especially as complex fluorides, significantly improves theproperties particularly of the coatings produced therewith.Surprisingly, the different additives thus function as in a modularsystem and make a substantial contribution to optimization of theparticular coating. In the specific case where a so-called multimetalmix is used, as often occurs in the pretreatment of car bodies and inthe treatment or pretreatment of different hardware or assembly parts,the aqueous composition according to the invention has proved verysuitable since the composition containing the various additives can bespecifically optimized to the particular multimetal mix and itspeculiarities and requirements.

With the process according to the invention, a mix of different metallicmaterials, e.g. as in the case of car bodies or different hardware, canbe coated with the aqueous coating in the same bath. Here, for example,any desired mix of substrates with metallic surfaces, selected from castiron, steel, aluminium, aluminium alloys, magnesium alloys, zinc andzinc alloys, can be coated simultaneously and/or successively accordingto the invention, it being possible for the substrates to be at leastpartially coated with metal and/or to consist at least partially of atleast one metallic material.

Provided at least one other component and/or traces of other substancesare not present, the remainder to 1000 g/l consists of water or of waterand at least one organic solvent such as ethanol, methanol, isopropanolor dimethylformamide (DMF). Preferably, in most embodiments, the organicsolvent content is particularly low or zero. Because of the hydrolysisof the at least one silane present, a content especially of ethanoland/or methanol can appear. It is particularly preferable not to add anyorganic solvent.

The composition is preferably free or substantially free of all types ofparticles, or particles with a mean diameter greater than 0.02 μm, whichmight be added e.g. in the form of oxides such as SiO₂.

The composition is preferably poor in, substantially free of or free oflarger contents or contents exceeding 1 g/l of water hardeners such ascalcium. The aqueous composition is preferably free of or poor in lead,cadmium, chromate, cobalt, nickel and/or other toxic heavy metals.Preferably, such substances are not deliberately added, although atleast one heavy metal, dissolved out of a metallic surface, can beentrained e.g. from another bath and/or can occur as an impurity. Thecomposition is preferably poor in, substantially free of or totally freeof bromide, chloride and iodide, since these can contribute to corrosionunder certain circumstances.

The layer thickness of the coatings produced according to the inventionranges preferably from 0.005 to 0.3 μm, particularly preferably from0.01 to 0.25 μm and very particularly preferably from 0.02 to 0.2 μm,and is frequently about 0.04 μm, about 0.06 μm, about 0.08 μm, about 0.1μm, about 0.12 μm, about 0.14 μm, about 0.16 μm or about 0.18 μm. Thecoatings containing organic monomer, oligomer, polymer, copolymer and/orblock copolymer are often somewhat thicker than those that are free oralmost free thereof.

Preferably, the composition forms a coating with a layer weight which,based only on the titanium and/or zirconium content, ranges from 1 to200 mg/m², calculated as elemental titanium. This layer weight rangesparticularly preferably from 5 to 150 mg/m² and very particularlypreferably from 8 to 120 mg/m² and, in particular, is about 10, about20, about 30, about 40, about 50, about 60, about 70, about 80, about90, about 100 or about 110 mg/m².

Preferably, the composition forms a coating with a layer weight which,based only on siloxanes/polysiloxanes, ranges from 0.2 to 1000 mg/m²,calculated as the corresponding extensively condensed polysiloxane. Thislayer weight ranges particularly preferably from 2 to 200 mg/m² and veryparticularly preferably from 5 to 150 mg/m² and, in particular, is about10, about 20, about 30, about 40, about 50, about 60, about 70, about80, about 90, about 100, about 110, about 120, about 130 or about 140mg/m².

If necessary, the coating produced with the aqueous compositionaccording to the invention can then be coated with at least one primer,lacquer or adhesive and/or with a lacquer-like organic composition,optionally at least one of these other coatings being cured by heatingand/or irradiation.

The metallic substrates coated by the process according to the inventioncan be used in the automobile industry, for railway vehicles, in theaerospace industry, in apparatus engineering, in mechanical engineering,in the building industry, in the furniture industry, for the manufactureof crash barriers, lamps, profiles, sheathing or hardware, for themanufacture of car bodies or body parts, individual components orpreassembled/connected elements, preferably in the automobile oraeronautical industry, or for the manufacture of appliances orinstallations, especially household appliances, control devices, testingdevices or structural elements.

An addition of manganese has surprisingly proved particularlyadvantageous: Although apparently no or almost no manganese compound isdeposited on the metallic surface, the addition greatly promotes thedeposition of silane/silanol/siloxane/polysiloxane on the metallicsurface. When adding nitroguanidine, it was found, surprisingly, thatthe optical characteristics of the coated metallic sheets are veryuniform, especially on sensitive surfaces such as sand-blasted iron orsteel surfaces. Unexpectedly, an addition of nitrite markedly reducedthe rusting tendency of steel substrates. It was found, surprisingly,that every addition mentioned in the present patent application ashaving a significantly positive effect has an additive effect onimproving the coating according to the invention: Choosing severaladditions, in a similar manner to a modular system, enables thedifferent properties, especially of a multimetal system, to be furtheroptimized.

It has now been found, surprisingly, that a good multimetal treatmentwith a single aqueous composition is only possible if a complex fluoridehas been used, and that a very good multimetal treatment with a singleaqueous composition is only possible if at least two different complexfluorides are used, e.g. those based on titanium and zirconium. In avery wide variety of experiments, the results obtained for complexfluorides used individually were never as good as those obtained for thecombination of these two complex fluorides, independently of what otheradditions were made.

The possibility of such a large increase in quality of aqueouscompositions containing silane/silanol/siloxane/polysiloxane could notbe anticipated. Surprisingly, however, a marked increase in the level ofquality in all tests was also found when using aqueous compositionsbased on a silane and only one titanium-based or zirconium-based complexfluoride (cf. Comparative Examples CE 3 and CE 4).

It was further surprising that, when testing the lacquer adhesion, stonechip resistance scores of 1 or 2 were obtained, even on steel: Steel hasproved to be the most problematic material for aqueous compositionsbased on a silane and only one titanium-based or zirconium-based complexfluoride, especially in terms of the corrosion resistance (cf., forexample, E 2).

In the case of aluminium and aluminium alloys, experience shows that theCASS test is problematic, but this also turned out markedly better thanexpected with the compositions according to the invention.

EXAMPLES AND COMPARATIVE EXAMPLES

The Examples according to the invention (E) and Comparative Examples(CE) described below are intended to illustrate the subject matter ofthe invention in greater detail.

The aqueous bath compositions are prepared as mixtures according toTable 1 using already prehydrolysed silanes. They each containpredominantly one silane and optionally also have small contents of atleast one other similar silane, where here again the word silane is usedrather than silane/silanol/siloxane/polysiloxane by way ofsimplification, and where normally these various compounds, sometimes ina larger number of similar compounds, also pass through into theformation of the coating, so there are often several similar compoundspresent in the coating as well. Depending on the silane, theprehydrolysis step can also take several days at room temperature, withvigorous stirring, if the silanes to be used are not already present inprehydrolysed form. The prehydrolysis of the silane is carried out byplacing the silane in excess water and optionally catalysing with aceticacid. Acetic acid was added in only a few embodiments for the solepurpose of adjusting the pH. In some embodiments, acetic acid is alreadypresent as a hydrolysis catalyst. Ethanol is formed in the hydrolysis,but is not added. The finished mixture is used fresh.

Then, for each test, at least 3 sheets of cold-rolled steel (CRS),aluminium alloy Al 6016, steel hot-dip galvanized or electrogalvanizedon both sides, or Galvaneal® (ZnFe layer on steel), previously cleanedwith an aqueous alkaline cleaner and rinsed with industrial water andthen with demineralised water, are brought into contact on both sideswith the appropriate pretreatment liquid in Table 1 at 25° C. byspraying, dipping or rollcoater treatment. The sheets treated in thisway were then dried at 90° C. PMT and subsequently lacquered with acathodic automobile dip lacquer (CDL). These sheets were then providedwith a complete commercial automotive lacquer system (filler, coveringlacquer, transparent lacquer; overall thickness of stacked layers,including CDL, approx. 105 μm) and tested for their corrosion protectionand lacquer adhesion. The compositions and properties of the treatmentbaths and the properties of the coatings are collated in Table 1.

The organofunctional silane A is an amino-functional trialkoxysilane andhas one amino group per molecule. Like all the silanes used here, it isin extensively or almost completely hydrolysed form in the aqueoussolution. The organofunctional silane B has one terminal amino group andone ureido group per molecule. The non-functional silane C is abis-trialkoxysilane; the corresponding hydrolysed molecule has up to 6OH groups on two silicon atoms. The polysiloxane D has a relativelyshort-chain molecule with a terminal OH group. It renders the coatinghydrophobic.

The complex fluorides of aluminium, silicon, titanium or zirconium areused extensively in the form of an MeF₆ complex, but the complexfluorides of boron are used extensively in the form of an MeF₄ complex.Manganese is added to the particular complex fluoride solution asmetallic manganese and dissolved therein. This solution is mixed withthe aqueous composition. If no complex fluoride is used, manganesenitrate is added. Copper is added as copper(II) nitrate and magnesium asmagnesium nitrate. Iron and zinc are mixed in as the nitrates. Nitrateon its own is preferably added as sodium nitrate or nitric acid. Epoxypolymer A contains OH⁻ and isocyanate groups and can thereforesubsequently be chemically crosslinked at temperatures above 100° C.Epoxy polymer B also contains OH⁻ and isocyanate groups and likewise cantherefore subsequently be chemically crosslinked at temperatures above100° C. Polymer B is more stable than polymer A in the bath when usingthe chosen compositions according to the invention. Silylated epoxypolymer C has a small content of OH⁻ and isocyanate groups and cantherefore also subsequently be chemically crosslinked at temperaturesabove 100° C.

The silanes present in the aqueous composition—concentrate and/orbath—are monomers, oligomers, polymers, copolymers and/or reactionproducts with other components due to hydrolysis reactions, condensationreactions and/or other reactions. The reactions take place especially inthe solution, during drying or optionally also during curing of thecoating, especially at temperatures above 70° C. All the concentratesand baths proved to be stable for one week without undergoing changes orprecipitations. No ethanol was added. Ethanol contents in thecompositions originated only from chemical reactions.

In the majority of Examples and Comparative Examples, the pH is adjustedwith ammonia if at least one complex fluoride is present and with anacid in other cases. All the baths have a good solution quality andalmost always a good stability. There are no precipitations in thebaths. After the coating step with the silane-containing solution, thecoating is firstly rinsed briefly once with demineralized water. Thecoated sheets are then dried at 120° C. in an oven for 5 minutes.Because of the interference colours, only the coatings on steel can besignificantly examined visually, allowing an assessment of thehomogeneity of the coating. The coatings without any complex fluoridecontent are very inhomogeneous. Surprisingly, a coating with titaniumcomplex fluoride and zirconium complex fluoride proved to be markedlymore homogeneous than when only one of these complex fluorides had beenapplied. An addition of nitroguanidine, nitrate or nitrite likewiseimproves the homogeneity of the coating. In some cases the layerthickness increases with the concentration of these substances.

TABLE 1 Bath compositions in g/l, based on solids contents or, in thecase of silanes, on the weight of the hydrolysed silanes; residualcontent: water and usually a very small amount of ethanol; process dataand properties of the coatings Example/CE CE CE CE CE E E E E E E 1 2 34 1 2 3 4 5 6 Organofunct. 0.2 — 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 silaneA Organofunct. — — — — — — — — — — silane B Non-funct. — 0.2 — — — — — —— — silane C H₂TiF₆ as Ti — — 0.2 — 0.1 0.1 0.5 0.5 0.3 0.2 H₂ZrF₆ as Zr— — — 0.2 0.1 0.5 0.1 0.5 0.3 0.2 Mn — — — — — — — — — — Acetic acid —0.02 — — — — — — — — pH 10.5 5 4 4 4 4 4 4 4 4 BMW cross-cut test: scoreSteel 4 3 5 3 2 0 1-2 1 1-2 2 E-zinc on steel 3 4 4 4 2 2 0 0 1 1-2Hot-dip zinc on 2 5 4 4 1-2 1 0 0 0 1 steel Al 6016 2 3 2 2 1-2 0 1 0 11 Galvaneal ® 1 2 1 2 1 0 0 0 0 1 10 VDA cycles, mm disbonding Steel 8 77 4 2 1.5 2.5 1.5 1.5 3 E-zinc on steel 5 5 3 4 1.5 2 1 1 1 2 Hot-dipzinc on 4 5 2.5 3.5 <1 <1 <1 <1 <1 <1 steel Galvaneal ® 2 3 2 1.5 <1 <1<1 <1 <1 <1 Stone chip resistance after VDA stress: score Steel 5 5 4 42-3 1 3 1 1 2-3 E-zinc on steel 5 5 3 4 2 2-3 1 1 1-2 2 Hot-dip zinc on5 5 3 4 2 2 1 1 1 1 steel Galvaneal ® 4 4 2 3 2 1 1 0 0 1-2 Salt spraytest, 1008 h Steel 7 8 4 3.5 3 2 2.5 2 1.8 2 CASS test, mm disbonding Al6016 6 5 3.5 3.5 3 3 2.5 2.5 2 2.5 Example/CE E E E E E E E E E CE 7 8 910 11 12 13 14 15 5 Organofunct. 0.2 0.2 0.2 0.2 0.1 0.3 0.2 0.1 — 0.2silane A Organofunct. — — — — — — — 0.1 — — silane B Non-funct. — — — —— — 0.1 — 0.2 — silane C H₂TiF₆ as Ti 0.3 0.3 0.2 0.4 0.2 0.2 0.2 0.20.2 — H₂ZrF₆ as Zr 0.2 0.4 0.3 0.3 0.2 0.2 0.2 0.2 0.2 — Mn — — — — — —— — — 0.3 Acetic acid — — — — — — 0.01 — — 0.35 pH 4 4 4 4 4 4 4 4 4 4.5BMW cross-cut test: score Steel 2 1 1 1 2 1 1 1 2 2-3 E-zinc on steel 10 1-2 0 2 1 2 0 2 3 Hot-dip zinc on 0 0 1 0 1 0 1 0 3 2 steel Al 6016 10-1 1 0 1 1 1 0 2 3 Galvaneal ® 0 0 1 0 1 0 0-1 0 1 2 10 VDA cycles, mmdisbonding Steel 3 1.5 2 1.5 2.5 2 2.5 1.8 3 7 E-zinc on steel 1.5 1.5 21.5 2.5 1.5 2 1 2.5 5 Hot-dip zinc on <1 <1 <1 <1 <1 <1 1 <1 2 4 steelGalvaneal ® <1 <1 <1 <1 <1 <1 1 0 0 3 Stone chip resistance after VDAstress: score Steel 2-3 2 1-2 1-2 2 1 2 1-2 3 5 E-zinc on steel 1 1 1-21 1-2 1 2 1 2 4 Hot-dip zinc on 1 1 1 0-1 1 0 1 1 1 4 steel Galvaneal ®1 0 0 0 1 0 1 1 1 4 Salt spray test, 1008 h Steel 2.5 2 2 2.5 3 2 2 1.52.5 7 CASS test, mm disbonding Al 6016 3 2.5 2 2 2.5 3 2 2.5 2 6Example/CE E E E E E E CE E 16 17 18 19 20 21 6 22 Organofunct. 0.2 0.20.2 0.2 0.2 0.2 0.2 0.2 silane A Non-funct. — — — 0.2 — — — — silane CH₂TiF₆ as Ti 0.2 0.2 0.2 0.2 0.2 0.2 — 0.2 H₂ZrF₆ as Zr 0.2 0.2 0.2 0.20.2 0.2 — 0.2 Mn 0.1 0.3 0.5 0.5 — 0.3 — — Cu — — — — 0.02 0.02 — — Mg —— — — — — — — Epoxy polymer A — — — — — — — — Silylated epoxy — — — — —— 1 1 polymer C Acetic acid — — — 0.02 — — — — pH 4 4 4 4 4 4 9 4 BMWcross-cut test: score Steel 2 1 1 3 1 1 3 1 E-zinc on steel 2 1 1 2 1 13 0 Hot-dip zinc on 1 0 0 0 0 0 4 0 steel Al 6016 1 1 1 0 1 1 2 1Galvaneal ® 1 1 0 0 1 1 2 0 10 VDA cycles, mm disbonding Steel 2 2 1.51.5 2 2 4 2.5 E-zinc on steel 1 1 1 1.5 1.5 1 4 1 Hot-dip zinc on 1 <1<1 <1 <1 <1 4 <1 steel Galvaneal ® <1 <1 <1 <1 0 <1 3 <1 Stone chipresistance after VDA stress: score Steel 2 1 1 1 1 1 4 1 E-zinc on steel1-2 1 1 2 1 1 4 1 Hot-dip zinc on 1 1 0-1 1 0 1 4 0 steel Galvaneal ® 11 1 2 0 1 3 0 Salt spray test, 1008 h Steel 2 1.5 1 2.5 2.5 1.5 3.5 1CASS test, mm disbonding Al 6016 2 1.5 1.5 1 2.8 2 5 1.5 Example/CE E CEE E E E E 23 7 24 25 26 27 28 Organofunct. 0.2 0.2 0.2 0.2 0.2 0.2 0.2silane A Non-funct. — — — — — — — silane C H₂TiF₆ as Ti 0.2 — 0.2 0.20.2 0.2 0.2 H₂ZrF₆ as Zr 0.2 — 0.2 0.2 0.2 0.2 0.2 Mn 0.3 — — 0.3 — 0.30.2 Cu — — — — — — — Mg — 0.3 — — 0.3 0.3 — Epoxy polymer A — 1 1 1 1 1— Silylated epoxy 1 — — — — — 1 polymer C Acetic acid — 0.3 — — — — — pH4 5 4 4 4 4 4 BMW cross-cut test: score Steel 0 3 1 0 2 1 0 E-zinc onsteel 0 3 0 0 2 1 0 Hot-dip zinc on 0 3 0 0 1 0 0 steel Al 6016 1 3 1 11 0 0 Galvaneal ® 0 2 0 0 1 0 0 10 VDA cycles, mm disbonding Steel 1.5 52 2 2.5 1.5 1.5 E-zinc on steel 1 4 1 <1 2 1 <1 Hot-dip zinc on <1 4 <1<1 1.5 <1 <1 steel Galvaneal ® <1 4 <1 <1 1 <1 <1 Stone chip resistanceafter VDA stress: score Steel 1 4 1-2 1-2 2-3 2 1 E-zinc on steel 1 41-2 1 2 1-2 1 Hot-dip zinc on 1 5 1 1 1 1 1 steel Galvaneal ® 1 3 1 1 11 1 Salt spray test, 1008 h Steel 0.5 5 1.5 1.5 2.5 2 1.5 CASS test, mmdisbonding Al 6016 1.5 6 1.5 1.5 2.5 2 1 Example/CE E E E E E E E E 2930 31 32 33 34 35 36 Organofunct. 0.2 0.2 0.2 0.2 0.1 — 0.2 0.1 silane AOrganofunct. — — — — 0.2 0.2 — — silane B Non-funct. — — — 0.1 — — — —silane C Polysiloxane D — — — — — — — — H₂TiF₆ as Ti 0.2 0.2 0.2 0.2 0.20.2 0.2 0.3 H₂ZrF₆ as Zr 0.2 0.2 0.2 0.2 0.2 0.2 — 0.3 Zr carbonate — —— — — — 0.2 — Mn 0.2 0.2 0.2 0.2 0.2 0.2 0.2 — Polymer B 0.1 0.5 2.5 — —— — — Acetic acid — — — 0.01 — — — — pH 4 4 4 4 4 4 4 4 BMW cross-cuttest: score Steel — — — — 1 1 — 2 E-zinc on steel — — — — 1 1 — 1Hot-dip zinc on — — — — 0-1 0-1 — 1 steel Al 6016 — — — — 1-2 1-2 — 1Galvaneal ® — — — — 1 1 — 0 10 VDA cycles, mm disbonding Steel — — — — 22 — 1.5 E-zinc on steel — — — — 1.5 1.5 — 1 Hot-dip zinc on — — — — 1 1— <1 steel Galvaneal ® — — — — 1 1 — <1 Stone chip resistance after VDAstress: score Steel — — — — 1 1 — 1-2 E-zinc on steel — — — — 1-2 1-2 —1-2 Hot-dip zinc on — — — — 1-2 1-2 — 1 steel Galvaneal ® — — — — 1-21-2 — 0-1 Salt spray test, 1008 h Steel — — — — 1.5 1.5 — 2 CASS test,mm disbonding Al 6016 — — — — 2 2 — 2 Example/CE E E E E E CE E E 37 3839 40 41 8 42 43 Organofunct. 0.1 0.6 0.6 0.1 — — 0.1 — silane AOrganofunct. — — — 0.2 0.2 — — — silane B Non-funct. — — — — — — — —silane C Polysiloxane D — — — — — — 0.1 0.2 H₂TiF₆ as Ti 0.3 0.1 0.1 0.20.2 0.2 0.2 0.2 H₂ZrF₆ as Zr 0.3 0.1 0.1 0.2 0.2 — 0.2 0.2 Zr carbonate— — — — — — — — Mn 0.2 — 0.2 0.3 0.3 — 0.3 0.3 Polymer B — — — — — — — —Acetic acid — — — — — — — — pH 4 4 4 4 4 4 4 4 BMW cross-cut test: scoreSteel — — — 0-1 0-1 — — — E-zinc on steel — — — 1 1 — — — Hot-dip zincon — — — 0 0 — — — steel Al 6016 — — — 1 1 — — — Galvaneal ® — — — 1 1 —— — 10 VDA cycles, mm disbonding Steel — — — 1.5 1.5 — — — E-zinc onsteel — — — 1 1 — — — Hot-dip zinc on — — — 1 1 — — — steel Galvaneal ®— — — <1 <1 — — — Stone chip resistance after VDA stress: score Steel —— — 0-1 0-1 — — — E-zinc on steel — — — 1 1 — — — Hot-dip zinc on — — —1 1 — — — steel Galvaneal ® — — — 1 1 — — — Salt spray test, 1008 hSteel — — — 1 1 — — — CASS test, mm disbonding Al 6016 — — — 1.5 1.5 — —— Example/CE E E CE CE E E E E 44 45 9 10 46 47 48 49 Organofunct. 0.20.2 0.2 0.2 0.2 0.2 0.2 0.2 silane A H₂TiF₆ as Ti — — — — — — 0.2 —H₂ZrF₆ as Zr — — — — — 0.2 — 0.2 H₃AlF₆ as Al 0.2 — — 0.2 0.2 0.2 0.2 —H₂BF₄ as B — 0.2 — 0.2 0.2 — — 0.2 H₂SiF₆ as Si — — 0.2 — — — — — Tinitrate — — — — — — — — Zr nitrate — — — — — — — — Mn 0.3 0.3 0.3 — 0.30.3 0.3 0.3 Fe — — — — — — — — Zn — — — — — — — — pH 4 4 4 4 4 4 4 4Example/CE E E E E E E E 50 51 52 53 54 55 56 Organofunct. 0.2 0.2 0.20.2 0.2 0.2 0.2 silane A H₂TiF₆ as Ti 0.2 — 0.2 0.2 0.2 0.2 0.2 H₂ZrF₆as Zr — — 0.2 0.2 0.2 0.2 0.2 H₃AlF₆ as Al — — — — — — — H₂BF₄ as B 0.2— — — — — — H₂SiF₆ as Si — — — — — — — Ti nitrate — 0.2 — — — — — Zrnitrate — 0.2 — — — — — Mn 0.3 0.3 0.5 — — — 1 Fe — — 2 1 — 2 2 Zn — — —— 1 1 1 pH 4 4 4 4 4 4 4

Over the short period of use, all the bath compositions are found to bestable and satisfactory to apply. There are no precipitations and nocolour changes, There are no differences in behaviour, visual impressionor test results between the different Examples and Comparative Exampleswhich can be attributed to the treatment conditions, e.g. application byspraying, dipping or rollcoater treatment. The films formed aretransparent and almost all are extensively homogeneous. They do notcolour the coating. The structure, gloss and colour of the metallicsurface appear to be only slightly changed by the coating. If a titaniumand/or zirconium complex fluoride is present, iridescent layers areformed, especially on steel surfaces. Combining several silanes has notso far brought about a significant improvement in the corrosionprotection, but this cannot be ruled out. Furthermore, a content ofH₃AlF₆ was found on aluminium-rich metallic surfaces due tocorresponding reactions in the aqueous composition. Surprisingly,however, combining two or three complex fluorides in the aqueouscomposition has proved extremely beneficial.

The layer thickness of the coatings produced in this way—also dependenton the type of application, which was initially varied in specificexperiments—ranged from 0.01 to 0.16 μm and usually from 0.02 to 0.12 μmand was often up to 0.08 μm, being markedly greater when organic polymerwas added.

The corrosion protection scores in the cross-cut test according to DINEN ISO 2409, after storage for 40 hours in 5% NaCl solution according toBMW specification GS 90011, range from 0 to 5, 0 representing the bestvalues. In the salt spray/condensation water alternation test over 10cycles according to VDA test sheet 621-415 with alternating corrosionstress between salt spray test, perspiration water test and dryinginterval, the disbonding is measured on one side from the scratchoutwards and reported in mm, the disbonding ideally being as small aspossible. In the stone chip resistance test according to DIN 55996-1,the coated metallic sheets are bombarded with scrap steel after theaforementioned VDA alternation test over 10 cycles: The damage pictureis characterized by scores from 0 to 5, 0 representing the best results.In the salt spray test according to DIN 50021 SS, the coated sheets areexposed for up to 1008 hours to an atomized corrosive sodium chloridesolution; the disbonding is then measured in mm from the scratchoutwards, the scratch being made with a standard gouge down to themetallic surface, and the disbonding ideally being as small as possible.In the CASS test according to DIN 50021 CASS, the coated sheets made ofan aluminium alloy are exposed for 504 hours to an atomized specialcorrosive atmosphere; the disbonding is then measured in mm from thescratch outwards and ideally is as small as possible.

Given that the development of the zinc/manganese/nickel phosphatizing ofcar bodies has spanned several decades, the phosphate layers of thistype produced today are of extremely high quality. Nevertheless,contrary to expectation, it was possible to achieve the samehigh-quality properties with silane-containing coatings by means ofaqueous silane-containing compositions that have only been in use for afew years, even though a greater effort was required.

Other experiments on car body elements have shown that theelectrochemical conditions of the CDL bath may be very slightlyadaptable to the different kind of coating, but otherwise that theoutstanding properties obtained in laboratory experiments can bereproduced on car body elements.

The invention claimed is:
 1. A process comprising coating a metallicsurface with a composition, wherein said composition consists of a) from0.02 to 1 g/L of at least one compound selected from the groupconsisting of a silane, a silanol, a siloxane and a polysiloxane,wherein the silane, the silanol, the siloxane or the polysiloxanecontains at least one group selected from the group consisting of anamino group, a urea group and a ureido group; b) at least two complexfluorides of formula MeF₆ wherein Me is a metal selected from the groupconsisting of titanium, hafnium, zirconium, aluminum and boron; water,and c) at least one cation selected from the group consisting of cerium,chromium, iron, calcium cobalt, copper, magnesium, manganese,molybdenum, nickel, niobium, tantalum, yttrium, zinc, and tin; whereinthe total amount of the complex fluorides ranges from 0.01 to 100 g/L.2. The process of claim 1, wherein prior to drying, at least one memberselected from the group consisting of a lacquer, a primer and anadhesive is applied to the coating.
 3. The process according to claim 1,further comprising the step of applying a lacquer, a lacquer-likecoating, a primer or an adhesive to the freshly applied silane-basedcoating that have not yet dried thoroughly.
 4. The process according toclaim 1, wherein the rinsing is conducted with demineralized water. 5.The process according to claim 1, wherein the coated surface is driedafter rinsing.
 6. The process according to claim 5, wherein the coatedsurface is dried after rinsing at a temperature of 120° C.
 7. Theprocess of claim 1, wherein the drying is conducted at a temperatureabove 70° C.
 8. A process comprising coating a plurality of metallicsurfaces in a bath of a composition consisting of a) at least onecompound selected from the group consisting of a silane, a silanol, asiloxane and a polysiloxane ranging from 0.02 to 1 g/L and wherein thesilane, the silanol, the siloxane or the polysiloxane has at least onemember selected from the group consisting of an amino group, a ureagroup GP and a ureido group; b) at least two complex fluorides offormula MeF₆ wherein Me is a metal selected from the group consisting oftitanium, hafnium, zirconium, aluminum and boron; water, c) at least onecation selected from the group consisting of cerium, chromium, iron,calcium cobalt, copper, magnesium, manganese, molybdenum, nickel,niobium, tantalum, yttrium, zinc, and tin, and d) at least one organiccompound selected from monomers, oligomers, polymers, copolymers andblock copolymers based on acrylic or urethane in a weight ratio of from1:0.05 to 1:2 of compounds based on silane, silanol, siloxane orpolysiloxane, calculated on the basis of the corresponding silanols, tocompounds based on organic polymers, calculated as added solids, in thecomposition, and and rinsing the coating when freshly applied and priorto thorough drying; wherein said plurality of metallic surfaces compriseat least two different metals and said plurality of surfaces are coatedin the same said bath, wherein the composition has a free fluoridecontent in the range of from 0.01 to 1 g/L, and wherein the total amountof the complex fluorides ranges from 0.01 to 100 g/L.
 9. The processaccording to claim 8, wherein said weight ratio is 1:0.05.
 10. Theprocess according to claim 8, wherein said weight ratio is 1:2.
 11. Aprocess comprising coating a metallic surface with a composition,wherein said composition consists of at least one silane, siloxane orpolysiloxane having at least one member selected from the groupconsisting of an amino group, a urea group and a ureido group; at leasttwo compounds complex fluorides of formula MeF₆ wherein Me is a metalselected from the group consisting of titanium, hafnium, zirconium,aluminum and boron; water, and at least one cation selected from thegroup consisting of cerium, chromium, iron, calcium cobalt, copper,magnesium, manganese, molybdenum, nickel, niobium, tantalum, yttrium,zinc, and tin, wherein the total amount of the complex fluorides rangesfrom 0.01 to 100 g/L.